By Nicholas Bakalar

Published: July 18, 2006

Smoking increases the risk of erectile dysfunction by 50 percent, and obesity nearly doubles the risk, new research suggests. Researchers tracked the diet and health of more than 22,000 male health professionals from all 50 states from 1986 through 2000.

At the start of the study, after controlling for other factors, they found that men with good or very good erectile function had a lower prevalence of smoking, a lower body mass index, and less hypertension, heart disease and diabetes than those who reported fair, poor or very poor function.

Among men who started with good or very good function, those who expended energy equivalent to running 1.5 hours a week reduced their risk of future erectile dysfunction by 30 percent compared with the group that exercised least.

But at any level of exercise, being overweight increased the risk of dysfunction. Men who were both overweight and physically inactive had a risk two and a half times that of men who were active and of normal weight.

The findings, published in the July issue of The Journal of Urology, were partially financed by Pfizer, and one of the six authors has a financial relationship with that company.

Smoking and obesity also increase the risk for heart disease, but they lead to erectile dysfunction at an earlier age, in time to begin preventive measures.

''The magnitude of risk is quite impressive,'' said Eric B. Rimm, an associate professor of epidemiology at Harvard and the senior author of the study. ''A 2 1/2-times risk if you're overweight and don't exercise should be a pretty strong incentive for people to start on a regular exercise program and lose weight.''